spi_flash: make {get,release}_temp_buffer OS functions optional

Fixes a crash when calling a NULL release_temp_buffer pointer throug
esp_flash_noos_functions, when doing a core dump.

components/spi_flash/esp_flash_api.c

@@ -562,8 +562,10 @@ esp_err_t IRAM_ATTR esp_flash_read(esp_flash_t *chip, void *buffer, uint32_t add
 
     if (!direct_read) {
         size_t actual_len = 0;
-        temp_buffer = chip->os_func->get_temp_buffer(chip->os_func_data, read_chunk_size, &actual_len);
-        read_chunk_size = actual_len;
+        if (chip->os_func->get_temp_buffer != NULL) {
+            temp_buffer = chip->os_func->get_temp_buffer(chip->os_func_data, read_chunk_size, &actual_len);
+            read_chunk_size = actual_len;
+        }
         if (temp_buffer == NULL) {
             return ESP_ERR_NO_MEM;
         }
@@ -600,7 +602,9 @@ esp_err_t IRAM_ATTR esp_flash_read(esp_flash_t *chip, void *buffer, uint32_t add
         buffer = (void*)((intptr_t)buffer + length_to_read);
     } while (err == ESP_OK && length > 0);
 
-    chip->os_func->release_temp_buffer(chip->os_func_data, temp_buffer);
+    if (chip->os_func->release_temp_buffer != NULL) {
+        chip->os_func->release_temp_buffer(chip->os_func_data, temp_buffer);
+    }
     return err;
 }
 

components/spi_flash/spi_flash_os_func_noos.c

@@ -70,19 +70,14 @@ static IRAM_ATTR esp_err_t delay_us(void *arg, unsigned us)
     return ESP_OK;
 }
 
-// Currently when the os is not up yet, the caller is supposed to call esp_flash APIs with proper
-// buffers.
-IRAM_ATTR void* get_temp_buffer_not_supported(void* arg, size_t reqest_size, size_t* out_size)
-{
-    return NULL;
-}
-
 const DRAM_ATTR esp_flash_os_functions_t esp_flash_noos_functions = {
     .start = start,
     .end = end,
     .delay_us = delay_us,
     .region_protected = NULL,
-    .get_temp_buffer = get_temp_buffer_not_supported,
+    /* the caller is supposed to call esp_flash_read/esp_flash_write APIs with buffers in DRAM */
+    .get_temp_buffer = NULL,
+    .release_temp_buffer = NULL,
     .yield = NULL,
 };